In chemistry, van der Waals strain is strain resulting from van der
Waals repulsion when two substituents in a molecule approach each
other with a distance less than the sum of their van der Waals radii.
Van der Waals strain is also called van der Waals repulsion and is
related to steric hindrance.[1] One of the most common forms of this
strain is eclipsing hydrogen, in Alkanes.
In rotational and pseudorotational mechanisms[edit]
In molecules whose vibrational mode involves a rotational or
pseudorotational mechanism (such as the
Berry mechanismBerry mechanism or the Bartell
mechanism),[2] van der Waals strain can cause significant differences
in potential energy, even between molecules with identical geometry.
PF5, for example, has significantly lower potential energy than PCl5.
Despite their identical trigonal bipyramidal molecular geometry, the
higher electron count of chlorine as compared to fluorine causes a
potential energy spike as the molecule enters its intermediate in the
mechanism and the substituents draw nearer to each other.
References[edit]